fix(chat): keep new session model authoritative

static/boot.js

@@ -1576,20 +1576,30 @@ function applyBotName(){
   // options are enough for first paint; the dynamic provider list can settle
   // after the saved session is visible.
   const _hydrateBootModelDropdown=()=>populateModelDropdown().then(()=>{
+    const sessionModelState=S.session&&S.session.model
+      ? {model:S.session.model,model_provider:S.session.model_provider||null}
+      : null;
     const savedState=(typeof _readPersistedModelState==='function')
       ? _readPersistedModelState()
       : (localStorage.getItem('hermes-webui-model')?{model:localStorage.getItem('hermes-webui-model'),model_provider:null}:null);
-    const savedModel=savedState&&savedState.model;
+    // Active sessions are authoritative. On fresh boot without a restored
-    // Guardrail: prefer profile/server default on boot when available.
+    // session, keep the profile/server default ahead of stale browser model
-    // Persisted browser model state should not override a valid default model.
+    // state when a default exists.
-    const allowBootSavedModelOverride=!window._defaultModel;
+    const stateToApply=sessionModelState||(!window._defaultModel?savedState:null);
-    if(savedModel && $('modelSelect') && allowBootSavedModelOverride){
+    const savedModel=stateToApply&&stateToApply.model;
+    if(savedModel && $('modelSelect')){
       const applied=(typeof _applyModelToDropdown==='function')
-        ? _applyModelToDropdown(savedModel,$('modelSelect'),savedState.model_provider||null)
+        ? (sessionModelState
+          ? _applyModelToDropdown(sessionModelState.model,$('modelSelect'),sessionModelState.model_provider||null)
+          : _applyModelToDropdown(savedState.model,$('modelSelect'),savedState.model_provider||null))
         : null;
-      if(!applied) $('modelSelect').value=savedModel;
+      if(!applied) $('modelSelect').value=stateToApply.model;
-      // If the value didn't take (model not in list), clear the bad pref
+      // If the value didn't take (model not in list), clear the bad pref only
-      if(!applied&&$('modelSelect').value!==savedModel){
+      // for persisted browser preferences. Active sessions remain authoritative.
+      if(!applied&&sessionModelState&&typeof _ensureModelOptionInDropdown==='function'){
+        _ensureModelOptionInDropdown(sessionModelState.model,$('modelSelect'),sessionModelState.model_provider||null);
+      }
+      else if(!applied&&!sessionModelState&&$('modelSelect').value!==stateToApply.model){
         if(typeof _clearPersistedModelState==='function') _clearPersistedModelState();
         else {
           localStorage.removeItem('hermes-webui-model');

static/sessions.js

@@ -490,8 +490,17 @@ async function newSession(flash, options={}){
       const sessionProvider=S.session.model_provider||null;
       const currentProvider=currentModelState.model_provider||null;
       if(S.session.model!==modelSel.value || sessionProvider !== currentProvider){
-        _applyModelToDropdown(S.session.model,modelSel,sessionProvider);
+        let sessionModelApplied=_applyModelToDropdown(S.session.model,modelSel,sessionProvider);
-        if(typeof syncModelChip==='function') syncModelChip();
+        if(!sessionModelApplied){
+          const opt=document.createElement('option');
+          opt.value=S.session.model;
+          opt.textContent=typeof getModelLabel==='function'?getModelLabel(S.session.model):S.session.model;
+          opt.dataset.custom='1';
+          opt.dataset.provider=sessionProvider||'';
+          modelSel.appendChild(opt);
+          sessionModelApplied=_applyModelToDropdown(S.session.model,modelSel,sessionProvider);
+        }
+        if(sessionModelApplied&&typeof syncModelChip==='function') syncModelChip();
       }
     }
     // Reset per-session visual state: a fresh chat is idle even if another

tests/test_new_chat_default_model_frontend.py

@@ -35,6 +35,27 @@ def test_new_chat_syncs_model_picker_when_default_provider_changes_but_model_id_
     assert "_applyModelToDropdown(S.session.model,modelSel,sessionProvider)" in fn
 
 
+def test_new_chat_inserts_session_model_when_static_picker_lacks_default():
+    fn = _new_session_function()
+    assert "sessionModelApplied" in fn
+    assert "document.createElement('option')" in fn
+    assert "opt.value=S.session.model" in fn
+    assert "opt.dataset.provider=sessionProvider||''" in fn
+    assert "modelSel.appendChild(opt)" in fn
+
+
+def test_boot_model_hydration_prefers_active_session_over_persisted_model():
+    boot_js = Path("static/boot.js").read_text(encoding="utf-8")
+    marker = "const sessionModelState=S.session&&S.session.model"
+    assert marker in boot_js
+    session_branch = boot_js[boot_js.index(marker) : boot_js.index("if(S.session) syncTopbar();", boot_js.index(marker))]
+    assert "_applyModelToDropdown(sessionModelState.model,$('modelSelect'),sessionModelState.model_provider||null)" in session_branch
+    assert "savedState" in session_branch
+    assert session_branch.index("sessionModelState") < session_branch.index("savedState"), (
+        "active session model must be considered before localStorage so stale saved model preferences cannot override new chats"
+    )
+
+
 def test_new_chat_does_not_send_stale_dropdown_model_when_session_has_default_model():
     assert "model:S.session.model||$('modelSelect').value" in MESSAGES_JS
     assert "model_provider:S.session.model_provider||null" in MESSAGES_JS